1. Field
The present disclosure relates generally to aircraft, and in particular, to controlling movement of the aircraft.
2. Background
Aircraft fly by displacing ambient air to generate lift. The aircraft may fly using static lift, dynamic lift, or some combination thereof. The aircraft also operates at many different altitudes. Further, the aircraft may operate with many different system constraints and flight conditions. The design of the aircraft often depends on what altitudes and speed the aircraft will fly at during operation of the aircraft. For example, a high-altitude, lighter-than-air aircraft flying at 100,000 feet at relatively slower speeds may employ propellers that are much longer, lower speed, and shaped differently than engine propeller aircraft used for general aviation. The difference in propeller design, in part, is due to a change in air density at the different operating altitudes. At higher altitudes, the density of the air is thinner. As a result, propellers designed for lower altitudes will not provide the performance needed at higher altitudes, such as altitudes from 50,000 to 125,000 feet.
As a result, the aircraft designed for one range of altitudes may not perform as well as desired at a different range of altitudes. Similarly, a vehicle design may not achieve maximum high altitude performance if the aircraft is also designed to take-off, land, operate, climb, and descend through lower altitudes with high density air, steady winds, and gusting winds. One solution involves using other secondary approaches to allow high-altitude long endurance (HALE) aircraft to reach higher altitudes. For example, secondary or supplemental propulsion, captive carriage on another vehicle, or towing by another vehicle may be employed.
For example, a high-altitude long endurance (HALE) aircraft is often carried by an aircraft or rocket close to the range of altitudes at which the HALE aircraft operates. This type of deployment of the aircraft may be more complex and expensive than desired.
Therefore, it would be desirable to have a method and apparatus that take into account at least some of the issues discussed above, as well as other possible issues. For example, it would be desirable to have a method and apparatus that overcomes a technical problem with controlling movement of the aircraft at the different altitudes.